Surface treatment method of group III nitride semiconductor and manufacturing method of the group III nitride semiconductor

ABSTRACT

There is provided a surface treatment method of a group III nitride semiconductor including: providing a group III nitride semiconductor including a first surface having a group III polarity and a second surface opposing the first surface and having a nitrogen polarity; and irradiating a laser beam onto the second surface to change the nitrogen polarity of the second surface to the group III polarity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.2008-0100773 filed on Oct. 14, 2008, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface treatment method of a groupIII nitride semiconductor, a group III nitride semiconductor, amanufacturing method of the same and a group III nitride semiconductorstructure, and more particularly, to a surface treatment method of agroup III nitride semiconductor in which opposing two surfaces haveidentical polarity, a group III nitride semiconductor, a manufacturingmethod of the same and a group III nitride semiconductor structure.

2. Description of the Related Art

In general, a light emitting device formed of a group III nitridesemiconductor is utilized to obtain light in a blue or green wavelength.The light emitting device is made of a semiconductor material having acomposition expressed by Al_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1, 0≦y≦1,and 0≦x+y≦1.

A group III nitride semiconductor can be grown on a heterogeneoussubstrate such as a sapphire (α-Al₂O₃) substrate and a SiC substrate.Particularly, the sapphire substrate has a hexagonal structure identicalto a gallium nitride. Moreover, the sapphire substrate is cheaper thanthe SiC substrate and stable at a high temperature, thus mainly employedas a growth substrate for the group III nitride semiconductor.

Meanwhile, the group III nitride semiconductor grown on the sapphiresubstrate has a Wurtzite and non-centrosymmetric crystal structure.Therefore, the group III nitride semiconductor, for example, gallium(Ga) nitride semiconductor has a gallium polarity on one surface(hereinafter gallium polarity surface and a nitrogen (N) polarity onanother surface (hereinafter nitrogen polarity surface). As describedabove, the two surfaces of the gallium nitride semiconductor experiencephysical differences in etching rate and surface recombinationconfiguration, or defects and surface dislocation due to differences insurface polarity. These physical differences lead to differences insurface characteristics between the gallium polarity surface and thenitrogen polarity surface.

Specifically, the gallium polarity surface of the gallium nitridesemiconductor exhibits a superior surface flatness than the nitrogenpolarity surface. Also, the gallium polarity surface possesses bettercrystallinity than the nitrogen polarity surface due to low binding ofmaterials acting as an impurity. Accordingly, when the galliumsemiconductor is re-grown, a re-growth layer grown on the galliumpolarity surface has a flat surface. Meanwhile, the re-growth layergrown on the nitrogen polarity surface suffers defects on a surfacethereof such as hillock, column and pyramidal grain.

In the meantime, polarity differences between both surfaces of thegallium nitride semiconductor cause spontaneous polarization, therebyleading to differences in surface band bending between the galliumpolarity surface and the nitrogen polarity surface.

Also, the gallium polarity surface of the gallium nitride semiconductorexhibits a low constant voltage due to low ohmic contact resistance, andpossesses superior electrical characteristics than the nitrogen polaritysurface. Moreover, the both surfaces of the gallium nitridesemiconductor react differently to an etching solution, for example,‘KOH’ owing to polarity differences. Specifically, the gallium polaritysurface hardly reacts with the etching solution and the nitrogenpolarity surface reacts actively with the etching surface and thus isetched significantly.

As described above, in a group III nitride semiconductor, a surfacehaving a group III polarity shows more superb characteristics than asurface having a nitrogen polarity in terms of surface flatness, bindingwith impurities, re-growth characteristics, electrical characteristicsand etching characteristics. Therefore, there is a call for developing agroup III nitride semiconductor whose opposing two surfaces have groupIII polarities.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a surface treatment methodin which a laser beam is irradiated onto a second surface opposing afirst surface with a group III polarity and having a nitrogen polarityto change the polarity of the second surface into an identical polarityto the first surface, a group III nitride semiconductor, a manufacturingmethod of the same and a group III nitride semiconductor structure.

According to an aspect of the present invention, there is provided asurface treatment method of a group III nitride semiconductor including:providing a group III nitride semiconductor including a first surfacehaving a group III polarity and a second surface opposing the firstsurface and having a nitrogen polarity; and irradiating a laser beamonto the second surface to change the nitrogen polarity of the secondsurface to the group III polarity.

The surface treatment method may further include forming a crystaldamage layer having a defect caused by nitrogen vacancies along thesecond surface, before the irradiating a laser beam onto the secondsurface. The forming a crystal damage layer may include performingplasma treatment or ion beam irradiation on the second surface.

The crystal damage layer may include at least one of an amorphous area,a poly-crystal area and a group III-rich area. The crystal damage layermay have a thickness of 5 to 2000 nm.

The group III nitride semiconductor may be a semiconductor representedby Al_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1.

The group III nitride semiconductor is a GaN semiconductor, and thegroup III polarity is a gallium polarity.

According to another aspect of the present invention, there is provideda method of manufacturing a group III nitride semiconductor, the methodincluding: growing a group III nitride semiconductor on a nitride singlecrystal growth substrate—wherein the group III nitride semiconductorincludes a first surface having a group III polarity and a secondsurface opposing the first surface, the second surface in contact withthe substrate and having a nitrogen polarity—; separating the group IIInitride semiconductor from the nitride single crystal growth substrate;and irradiating a laser beam onto the second surface to change thenitrogen polarity of the second surface to a group III polarity.

The method may further include forming a crystal damage layer having adefect caused by nitrogen vacancies along the second surface, before theirradiating a laser beam onto the second surface. The forming a crystaldamage layer may include performing plasma treatment or ion beamirradiation onto the second surface.

The crystal damage layer may include at least one of an amorphous area,a poly-crystal area and a group III-rich area. The crystal damage layermay have a thickness of 5 to 2000 nm. The group III nitridesemiconductor may be a semiconductor represented byAl_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1. The groupIII nitride semiconductor may be a GaN semiconductor, and the group IIIpolarity is a gallium polarity.

The method may further include growing an additional nitridesemiconductor layer on the second surface changed to have the group IIIpolarity.

The nitride single crystal growth substrate may be formed of a materialselected from a group consisting of sapphire, SiC, Si, ZnO, MgAl₂O₄,MgO, LiAlO₂ and LiGaO₂.

According to still another aspect of the present invention, there isprovided a group III nitride semiconductor including a first surfacehaving a group III polarity and a second surface opposing the firstsurface, the group III nitride semiconductor including: a polarityinversion layer corresponding to an area of the group III nitridesemiconductor layer located along the second surface, and formedcontinuously with the other area of the group III nitride semiconductorlayer, the polarity inversion layer having a crystal arrangement of theother area inversed such that the second surface has a group IIIpolarity identical to a polarity of the first surface. The polarityinversion layer may have a thickness of 5 to 2000 nm.

The area corresponding to the polarity inversion layer may have acomposition identical to a composition of the other area.

The group III nitride semiconductor may be a semiconductor representedby Al_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1.

The group III nitride semiconductor may be a GaN semiconductor, and thegroup III polarity may be a gallium polarity.

According to yet another aspect of the present invention, there isprovided a group III nitride semiconductor structure including: a firstgroup III nitride semiconductor including a first surface having a groupIII polarity and a second surface opposing the first surface; and asecond group III nitride semiconductor formed on the second surface ofthe first group III nitride semiconductor, wherein the first group IIInitride semiconductor includes a polarity inversion layer correspondingto an area of the first group III nitride semiconductor layer locatedalong the second surface, and formed continuously with the other area ofthe first group III nitride semiconductor, the polarity inversion layerhaving a crystal arrangement of the other area inversed such that thesecond surface has a group III polarity identical to a polarity of thefirst surface. The polarity inversion layer may have a thickness of 5 to2000 nm.

The area corresponding to the polarity inversion layer may have acomposition identical to a composition of the other area of the firstgroup III nitride semiconductor.

The second group III nitride semiconductor may have a compositiondifferent from a composition of the first group III nitridesemiconductor or a conductivity type different from a conductivity typeof the first group III nitride semiconductor.

The second group III nitride semiconductor may include a plurality ofgroup III nitride semiconductor layers each including an active layer,and the group III nitride semiconductor structure includes asemiconductor light emitting device.

The first group III nitride semiconductor may be a semiconductorrepresented by Al_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1, 0≦y≦1, and0≦x+y≦1.

The first group III nitride semiconductor may be a GaN semiconductor,and the group III polarity may be a gallium polarity.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1A to 1D illustrate a surface treatment method of a group IIInitride semiconductor according to an exemplary embodiment of theinvention;

FIGS. 2A to 2E illustrate a method of manufacturing a group III nitridesemiconductor according to an exemplary embodiment of the invention;

FIG. 3 illustrates a group III nitride semiconductor structure accordingto an exemplary embodiment of the invention;

FIG. 4 is a photograph illustrating a group III nitride semiconductormanufactured by the method shown in FIGS. 2A to 2E;

FIG. 5 is a photograph illustrating a group III nitride semiconductorhaving one surface etched according to an exemplary embodiment of theinvention;

FIG. 6 illustrates a group III nitride semiconductor light emittingdevice according to an exemplary embodiment of the invention; and

FIG. 7 is a graph illustrating characteristics of a group III nitridesemiconductor device shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIGS. 1A to 1D illustrate a surface treatment method of a group IIInitride semiconductor according to an exemplary embodiment of theinvention. First, as shown in FIG. 1A, a group III nitride semiconductor10 is provided. Here, the group III nitride semiconductor 10 may be asingle crystal layer substrate having a semiconductor compositionexpressed by Al_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1.The group III nitride semiconductor 10 may be a single crystal substratehaving a GaN semiconductor composition.

Also, the group III nitride semiconductor 10 includes a first surface 11having a group III polarity and a second surface 12 opposing the firstsurface and having a nitrogen polarity. Specifically, in the group IIInitride semiconductor, group III elements and nitrogen elements have aWurtzite crystal structure. The group III elements are arranged on thefirst surface 11 and the nitrogen elements are arranged on the secondsurface 12. That is, the first surface 11 and the second surface 12 havepolarities according to the elements arranged thereon, respectively.

Hereinafter, a surface treatment process in which the second surface 12is changed from a nitrogen polarity to a group III polarity will bedescribed in detail.

Referring to FIG. 1B, a crystal damage layer 13 with defects caused bynitrogen vacancies is formed on the second surface 12. Here, the crystaldamage layer 13 may be one of an amorphous area, a poly-crystal area anda group III-rich area. The second surface 12 can be formed by performingplasma treatment or ion beam irradiation.

As described above, when the second surface 12 is plasma-treated orirradiated with ion beam, nitrogen vacancies are generated in a layerreaching a certain thickness from the second surface 12 to thereby forma crystal damage layer 13 where the group III elements and the nitrogenelements are arranged irregularly. The crystal damage layer 13 may beformed to a thickness of 5 to 2000 nm from the second surface 12.

Thereafter, as shown in FIG. 1C, a laser beam is irradiated to change apolarity of the second surface 12 into a group III polarity.Specifically, a laser beam is irradiated onto the crystal damage layer13 reaching a certain thickness from the second surface 12. Then, thegroup III elements and nitrogen elements arranged randomly on thecrystal damage layer 13 are re-crystallized. Accordingly, this changes acrystal arrangement of the group III elements and nitrogen elements inthe crystal damage layer 13, thus allowing the group III elements, notnitrogen elements to be arranged on the second surface 12. That is, thesecond surface 12 is changed to have a group III polarity. This isbecause the group III elements are arranged more stably on the surfacethan the nitrogen elements. Therefore, the second surface 12 has a groupIII polarity with a relatively stable crystal structure duringre-crystallization of the group III elements and nitrogen elements.

The processes described above produce a group III nitride semiconductor10′0 as shown in FIG. 1D. Specifically, the group III nitridesemiconductor 10′ shown in FIG. 1D includes a first surface 11 having agroup III polarity and a second surface 12 opposing the first surface 11and having a group III polarity. Also, the group III nitridesemiconductor 10′ includes a polarity inversion layer 13′.

The polarity inversion layer 13′ corresponds to an area of the group IIInitride semiconductor 10′ located along the second surface 12. Thepolarity inversion layer 13′ is not formed separately from the group IIInitride semiconductor 10′ but formed to be continuous with the otherarea of the group III nitride semiconductor 10′.

As described above, the group III nitride semiconductor 10′ shown inFIG. 1D may be structured such that the first surface 11 and the secondsurface opposite to each other with respect to the polarity inversionlayer 13′ have an identical group III polarity.

FIGS. 2A to 2E illustrate a method of manufacturing a group III nitridesemiconductor according to an exemplary embodiment of the invention.Referring to FIG. 2A, the group III nitride semiconductor 100 is grownon a nitride single crystal growth substrate 200 in an arrow direction.Here, the nitride single crystal growth substrate 200 may be formed of amaterial selected from a group consisting of sapphire, SiC, Si, ZnO,MgAl₂O₄, MgO, LiAlO₂ and LiGaO₂. Also, the group III nitridesemiconductor 100 may be formed on the substrate 200 by one ofmetal-organic chemical vapor deposition (MOCVD), hydride vapor phaseepitaxy (HVPE), and molecular beam epitaxy (MBE).

The group III nitride semiconductor 100 grown in FIG. 2A may have acomposition expressed by Al_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1, 0≦y≦1,and 0≦x+y≦1. Therefore, the group III nitride semiconductor 100 has acrystal structure in which at least one group III element out ofaluminum (Al), indium (In) and gallium (Ga) and a nitride element arebound together at a uniform interval. Moreover, the group III nitridesemiconductor 100 may have a GaN semiconductor composition containingthe gallium element and the nitride element.

Meanwhile, the group III nitride semiconductor 100 grown as in FIG. 2Aincludes a first surface 110 and a second surface 120 in contact withthe nitride single crystal growth substrate 200 and opposing the firstsurface 110. Here, the first surface 110 has group III elements arrangedthereon and thus has a group III polarity. The second surface 120 hasnitrogen elements arranged thereon and thus has a nitrogen polarity.

More specifically, the first surface 110 and the second surface 120 ofthe group III nitride semiconductor 100 have a crystal structure suchthat gallium elements as the group III element and nitrogen elements arearranged periodically. At this time, the first surface 110 of the groupIII nitride semiconductor 100 has the gallium elements arranged thereon,thus exhibiting a gallium polarity. Meanwhile, the second surface 120 incontact with the nitride single crystal substrate 200 has the nitrogenelements arranged thereon, thus showing a nitrogen polarity.

Thereafter, when the group III nitride semiconductor 100 is grown, asshown in FIG. 2B, a laser beam is irradiated onto the nitride singlecrystal growth substrate 200 to separate the group III nitridesemiconductor 100 from the nitride single crystal growth substrate 200.Accordingly, this exposes the second surface 120 of the group IIInitride semiconductor 100 where the nitride single crystal growthsubstrate 200 is bonded.

Next, the processes shown in FIGS. 2C and 2D are employed to change apolarity of the second surface 120 of the group III nitridesemiconductor 100. For convenience of description, FIGS. 2C and 2Dillustrate the group III nitride semiconductor 100 of FIG. 2B that isrotated such that the second surface 120 faces upward.

As shown in FIG. 2C, the crystal damage layer 130 is formed on thesecond surface 120 of the group III nitride semiconductor 100. Here, thecrystal damage layer 130 includes defects caused by nitrogen vacanciesand has a crystal structure where group III elements and nitrogenelements are randomly arranged. That is, the crystal damage layer 130may be at least one of an amorphous area, a poly-crystal area and agroup III-rich area.

The crystal damage layer 130 may be formed on the second surface 120 byperforming plasma treatment or ion beam irradiation. The crystal damagelayer 130 may have a thickness of 5 to 2000 nm by adjusting time andcondition of the plasma treatment or ion beam irradiation.

Afterwards, as shown in FIG. 2D, a laser beam is irradiated onto thecrystal damage layer 130 to change the nitrogen polarity of the secondsurface 120 to a group III polarity. Specifically, laser beamirradiation re-crystallizes the group III elements and nitrogen elementsarranged randomly on the crystal damage layer 130. Accordingly, thisallows the group III elements and nitrogen elements in the crystaldamage layer 130 to be re-arranged and the group III elements to bearranged on the second surface 120. That is, the second surface 120 ischanged to have the group III polarity.

Referring to FIG. 2D, a laser utilized to re-arrange the group IIIelements and nitrogen elements in the crystal damage layer 130 mayemploy a 193 nm excimer laser, a 248 nm excimer laser, a 308 nm excimerlaser, a Nd:YAG laser, a He—Ne laser, and an Ar ion laser.

Meanwhile, to re-arrange the group III elements and nitrogen elements inthe crystal damage layer 130, in addition to the laser beam irradiation,a predetermined heat may be applied to the crystal damage layer 130using ion beam or annealing to allow the group III elements and nitrogenelements to be re-arranged.

The processes shown in FIGS. 2A to 2D can produce a group III nitridesemiconductor 100′ shown in FIG. 2E. Specifically, the group III nitridesemiconductor 100′ shown in FIG. 2E includes a first surface 110 havinga group III polarity, a second surface 120 opposing the first surface110 and having a group III polarity and a polarity inversion layer 130′formed to a certain thickness from the second surface 120.

The polarity inversion layer 130′ of FIG. 2E corresponds to an area ofthe group III nitride semiconductor 100′ located along the secondsurface 120. That is, the polarity inversion layer 130′ is not formedseparately from the group III nitride semiconductor 100′ but formed tobe continuous with the group III nitride semiconductor 100′ through asingle growth process of the group III nitride semiconductor as shown inFIG. 2A, and thus is continuous with the other area. Here, the otherarea may cover an area from an area opposing the second surface 120,i.e., the first surface 110 to a boundary of the polarity inversionlayer 130′.

Furthermore, the polarity inversion layer 130′ may have a crystalarrangement of the other area inversed such that the second surface 120has a group III polarity identical to a polarity of the first surface110. That is, the polarity inversion layer 130′ is re-crystallized suchthat the group III elements and nitrogen elements of the crystal damagelayer 130 shown in FIGS. 2C and 2D are inversed in crystal arrangement.This polarity inversion layer 130′ may have a thickness of 5 to 2000 nm.

Meanwhile, the group III nitride semiconductor 100′ is re-crystallizedwith the second surface 120 of the group III nitride semiconductor 100′of FIG. 2E as a growth surface, thereby producing a group III nitridesemiconductor structure having crystallinity and surface flatness. Thiswill be described in detail hereafter.

FIG. 3 illustrates a group III nitride semiconductor structure accordingto an exemplary embodiment of the invention. Referring to FIG. 3, thegroup III nitride semiconductor structure 500 includes a first group IIInitride semiconductor 100′ and a second group III nitride semiconductor100′-1.

The first group III nitride semiconductor 100′ is identical to the groupIII nitride semiconductor 100′ shown in FIG. 2E. The first group IIInitride semiconductor 100′ includes a first surface 110 having a groupIII polarity and a second surface 120 opposing the first surface 110.Also, the first group III nitride semiconductor 100′ includes a polarityinversion layer 130′ corresponding to an area located along the secondsurface 120 and having a crystal arrangement of the other area inversed'such that the second surface 120 has a polarity identical to a polarityof the first surface 110.

The second group III nitride semiconductor 100′-1 is formed on thesecond surface 120 of the first group III nitride semiconductor 100′.Here, the second group III nitride semiconductor 100′-1 may be formed byone of metal organic chemical vapor deposition (MOCVD), hydride vaporphase epitaxy (HVPE) and molecular beam epitaxy (MBE). Also, the secondgroup III nitride semiconductor 100′-1 may have a semiconductorcomposition identical to or different from the first group III nitridesemiconductor 100′.

As described above, the second group III nitride semiconductor 100′-1 isformed on the second surface 120 having a group III polarity, and thusis reduced in defects such as hillock, column and pyramidal grain.Accordingly, when compared with a case where the second group IIInitride semiconductor 100′-1 is grown on the surface having a nitrogenpolarity, the second group III nitride semiconductor 100′-1 is improvedin crystallinity and surface flatness.

Meanwhile, referring to FIG. 3, the second group III nitridesemiconductor 100′-1 is illustrated as a single layer but may be aplurality of group III nitride semiconductor layers each including anactive layer. That is, the plurality of group III nitride semiconductorlayers are grown on the second surface 120 of the first group IIInitride semiconductor 100′ to produce a semiconductor light emittingdevice. Here, the semiconductor light emitting device manufactured usingthe second surface 120 having the group III polarity is superior incrystallinity and thus increased in light emitting efficiency.

FIG. 4 is a photograph illustrating a group III nitride semiconductormanufactured by the method shown in FIGS. 2A to 2E. Specifically, FIG. 4is a cross-section obtained by vertically cutting and photographing agroup III nitride semiconductor 100′. That is, FIG. 4 illustrates acrystal arrangement of a first surface 110 which is a bottom surface ofthe group III nitride semiconductor and a second surface 120 which is atop surface of the group III nitride semiconductor.

The group III nitride semiconductor 100′ is a GaN semiconductor and boththe first surface 110 and the second surface 120 have a galliumpolarity. Here, the second surface 120 is a layer having a galliumpolarity due to a polarity inversion layer 130′ having a polarityinversed by crystal re-arrangement of gallium elements and nitrogenelements.

Meanwhile, referring to the crystal arrangement shown in FIG. 4, an Aportion represents polarity of the first surface 110 and a C portionrepresents polarity of the second surface 120. Moreover, a B portion anda D portion represent polarities bound with corresponding polarities ofthe A portion and the C portion, respectively.

First, it is observed that the A portion and C portion corresponding toboth surfaces of the group III nitride semiconductor 100′ have (0002)plane indicating a gallium polarity. That is, the gallium polarity isformed toward the opposing two surfaces of the group III nitridesemiconductor 100′. Also, the B portion and the D portion have (000-2)plane indicating a nitrogen polarity. That is, the group III nitridesemiconductor 100′ has a crystal arrangement in which the galliumpolarity and the nitrogen polarity are combined together. But the firstsurface 110 and the second surface 120 exhibit a gallium polarity.

FIG. 5 is a photograph illustrating a group III nitride semiconductorhaving one surface etched according to an exemplary embodiment of theinvention. Specifically, the nitride semiconductor 300 shown in FIG. 5is a GaN semiconductor and a first area 310 located left from the A-A′line is a surface-treated area using the method of FIGS. 1B and 1C, thatis, an area obtained by etching a gallium polarity area through polarityinversion. Meanwhile, a second area 320 located in the right side is anarea which is not surface-treated and obtained by etching a nitrogenpolarity area.

The group III nitride semiconductor 300 is etched under identicalconditions, for example, etching temperature and etching time, using aKOH etching solution. As a result, the first area 310 with a galliumpolarity is hardly etched and the second area 320 with a nitrogenpolarity has a surface etched to form an irregular rough structure. Asdescribed above, it is clearly shown that the polarity of the first area310 is changed to the gallium polarity by etching the first area 310 andthe second area 320.

FIG. 6 illustrates a group III nitride semiconductor light emittingdevice according to an exemplary embodiment of the invention.

The group III nitride semiconductor 400 shown in FIG. 6 is a GaNsemiconductor and includes a light emitting structure having a first GaNsemiconductor layer 411, an active layer 412 and a second GaNsemiconductor layer 413. The group III nitride semiconductor 400includes a first electrode 420 in contact with the first GaNsemiconductor layer 411 and a second electrode 430 formed on the secondGaN semiconductor layer 413 and has a vertical structure. Here, bothsurfaces of the light emitting structure, i.e., one surface of the firstGaN semiconductor layer 411 and one surface of the second GaNsemiconductor layer 413 have a gallium polarity. That is, the firstelectrode 420 and the second electrode 430 are formed on the lightemitting structure having a gallium polarity.

The group III nitride semiconductor 400 shown in FIG. 6 can bemanufactured as follows. First, the first GaN semiconductor layer 411,the active layer 412 and the second GaN semiconductor layer 413 aresequentially stacked on a nitride single crystal substrate such as asapphire substrate to form the light emitting structure. Also, thesecond electrode 430 is formed on the second GaN semiconductor layer413. Moreover, although not shown, a conductive support substrate may befurther provided on the second electrode 430 to support the lightemitting structure.

Thereafter, the light emitting structure is separated from the nitridesingle crystal substrate by general laser lift-off. In this lightemitting structure, a surface 411 a of the first GaN semiconductor layer411 bonded to the nitride single crystal growth substrate may have anitrogen polarity and a surface 413 a of the second GaN semiconductorlayer 413 located in an uppermost part may have a gallium polarity. Thatis, the two opposing surfaces of the light emitting structure havedifferent polarities from each other.

To ensure that the both surfaces of this light emitting structure have agallium polarity, the surface 411 a of the first GaN semiconductor layer411 having a nitrogen polarity is surface-treated. Specifically, asshown in FIGS. 1B and 1C, a crystal damage layer is formed on thesurface 411 a of the first GaN semiconductor layer 411 and then a laserbeam is irradiated thereonto so that the surface 411 a is inversed inpolarity to have a gallium polarity.

Thereafter, the first electrode 420 is formed on the surface 411 a ofthe first GaN semiconductor layer 411 having a gallium polarity toproduce a group III nitride semiconductor light emitting device 400shown in FIG. 6. At this time, an entire portion of the surface 411 a ofthe first GaN semiconductor layer 411 may have a gallium polarity.Alternatively, only a portion of the surface 411 a where the firstelectrode 420 is to be formed may have a gallium polarity. Here, thesurface 411 a of the first GaN semiconductor layer 411 has a crystalarrangement having both a gallium polarity and a nitrogen polarity.

The light emitting structure shown in FIG. 6 include the two surfaces411 a and 413 a having a gallium polarity. The light emitting structureis improved in spontaneous polarization caused by polarity differencesbetween the two surfaces. Accordingly, surface band bendingcharacteristics are shown similarly at the both surfaces having agallium polarity. Also, the light emitting structure is low in ohmiccontact resistance to reduce constant voltage and leakage current. Thisleads to improvement in electrical properties of the nitridesemiconductor light emitting device 400. This will be described indetail hereinafter.

FIG. 7 is a graph illustrating current-voltage characteristics of agroup III nitride semiconductor device shown in FIG. 6. Referring toFIG. 7, a first graph 1 illustrates current-voltage characteristics of agroup III nitride semiconductor light emitting device manufactured by aconventional method. A second graph 2 illustrates current-voltagecharacteristics of the group III nitride semiconductor light emittingdevice 400 shown in FIG. 6. Specifically, the first graph 1 and thesecond graph 2 each illustrate a measurement of a current changing inresponse to a voltage after applying the voltage to the light emittingdevice.

In the art, an ideal current-voltage of the semiconductor light emittingdevice has non-linear characteristics. That is, a very low current flowsat a negative voltage and a weak positive voltage and a currentincreases rapidly at a predetermined level of voltage (about 0.7V ormore).

Meanwhile, the general group III nitride semiconductor light emittingdevice having voltage-current characteristics shown in the first graph(1) is structured identically to the group III nitride semiconductorlight emitting device 400 shown in FIG. 6, but a light emittingstructure of the general light emitting device has different polaritieson both surfaces thereof. That is, one surface of the light emittingstructure has a gallium polarity and another surface opposing the onesurface has a nitrogen polarity. Here, in the light emitting structure,an electrode formed on the another surface with a nitrogen polarity ishigh in ohmic contact resistance to thereby generate constant voltageand leakage current. Accordingly, the general group III nitridesemiconductor light emitting device has current-voltage characteristicssuch that a low current flows only in a voltage range of −0.5 to 0.5V asin the first graph 1 and a high current flows in the other voltagerange, thereby generating a leakage current.

Meanwhile, the group III nitride semiconductor light emitting device 400of FIG. 6 has non-linear current-voltage characteristics such that as ina second graph (2), a low current flows at a negative voltage and acurrent rapidly increases in a voltage range of 1 to 2V. This is similarto ideal current-voltage characteristics. Therefore, the group IIInitride semiconductor light emitting device of the present inventionallows a constant voltage and leakage current to be reduced to therebyimprove electrical properties.

As set forth above, in a group III nitride semiconductor manufactured bythe method according to exemplary embodiments of the invention, a laserbeam is irradiated onto a second surface with a nitrogen polarityopposing a first surface with a group III element polarity so that thesecond surface is changed to have an identical polarity to the firstsurface. This allows the opposing surfaces of the group III nitridesemiconductor to have an identical group III element polarity.

When a semiconductor structure such as a light emitting device ismanufactured using a second surface surface-treated to have a group IIIpolarity in a group III nitride semiconductor, the light emitting deviceis improved in crystallinity and thus enhanced in light emittingefficiency.

Moreover, when the group III nitride semiconductor is re-grown using thesecond surface surface-treated to have a group III polarity, a re-growthlayer with superior surface flatness can be formed.

Also, when an electrode is formed on the second surface surface-treatedto have a group III polarity of the group III nitride semiconductor, anohmic contact resistance at a contact surface is reduced to improveelectrical properties.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A surface treatment method of a group III nitride semiconductorcomprising: providing a group III nitride semiconductor including afirst surface having a group III polarity and a second surface opposingthe first surface and having a nitrogen polarity; forming a crystaldamage layer having a defect caused by nitrogen vacancies along thesecond surface; and irradiating a laser beam onto the second surface tochange the nitrogen polarity of the second surface to the group IIIpolarity.
 2. The surface treatment method of claim 1, wherein theforming a crystal damage layer comprises performing plasma treatment orion beam irradiation on the second surface.
 3. The surface treatmentmethod of claim 1, wherein the crystal damage layer comprises at leastone of an amorphous area, a poly-crystal area and a group III-rich area.4. The surface treatment method of claim 1, wherein the crystal damagelayer has a thickness of 5 to 2000 nm.
 5. The surface treatment methodof claim 1, wherein the group III nitride semiconductor is asemiconductor represented by Al_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1,0≦y≦1, and 0≦x+y≦1.
 6. The surface treatment method of claim 1, whereinthe group III nitride semiconductor is a GaN semiconductor, and thegroup III polarity is a gallium polarity.
 7. A method of manufacturing agroup III nitride semiconductor, the method comprising: growing a groupIII nitride semiconductor on a nitride single crystal growth substrate,wherein the group III nitride semiconductor includes a first surfacehaving a group III polarity and a second surface opposing the firstsurface, the second surface in contact with the substrate and having anitrogen polarity; separating the group III nitride semiconductor fromthe nitride single crystal growth substrate; forming a crystal damagelayer having a defect caused by nitrogen vacancies along the secondsurface; and irradiating a laser beam onto the second surface to changethe nitrogen polarity of the second surface to a group III polarity. 8.The method of claim 7, wherein the forming a crystal damage layercomprises performing plasma treatment or ion beam irradiation onto thesecond surface.
 9. The method of claim 7, wherein the crystal damagelayer comprises at least one of an amorphous area, a poly-crystal areaand a group III-rich area.
 10. The method of claim 7, wherein thecrystal damage layer has a thickness of 5 to 2000 nm.
 11. The method ofclaim 7, wherein the group III nitride semiconductor is a semiconductorrepresented by Al_(x)In_(y)Ga_((1−x−y))N, where 0≦x≦1, 0≦y≦1, and0≦x+y≦1.
 12. The method of claim 7, wherein the group III nitridesemiconductor is a GaN semiconductor, and the group III polarity is agallium polarity.
 13. The method of claim 7, further comprising growingan additional nitride semiconductor layer on the second surface changedto have the group III polarity.
 14. The method of claim 7, wherein thenitride single crystal growth substrate is formed of a material selectedfrom a group consisting of sapphire, SiC, Si, ZnO, MgAl₂O₄, MgO, LiAlO₂and LiGaO₂.